Method for transmitting and receiving control information of a mobile communication system

ABSTRACT

Disclosed is a method for transmitting and receiving control information. The method for transmitting control information according to the present invention, in a mobile communication system in which a control channel region and a data channel region are separated from each other, comprises the steps of: determining a control channel resource for transmitting control information by means of the data channel region; and transmitting the control information using the determined control channel resource. According to the present invention, a capacity for control information, which increases for multiple user multiple-input multiple-out (MIMOs) in a heterogeneous network environment, for heterogeneous network interference control using carrier aggregation, for frequent use of a multicast-broadcast single frequency network (MBSFN) subframe, and for a CoMP transmission control, may be satisfied. Further, an adaptive resource allocation based on a requested capacity for control information may be enabled, and the efficient utilization of resources may also be enabled.

TECHNICAL FIELD

The following description relates to a mobile communication system, andmore particularly, to a method of transmitting and receiving controlinformation such as uplink or downlink scheduling information, etc. of amobile communication system.

BACKGROUND ART

A conventional cellular mobile communication system based on 3GPP LTEtransmits a downlink control channel by assigning time-frequencyresources to an area for transmitting downlink control information. Inother words, the conventional cellular mobile communication system usesa method of transmitting control information using one to three OFDMsymbols located in the beginning portion of each subframe.

However, due to Multi-user Multiple Input Multiple Output (MU-MIMO)technology in a heterogeneous network environment, control ofinterference between heterogeneous networks using Carrier Aggregation,frequent use of Multicast-Broadcast Single Frequency Network (MBSFN)subframes, technology of transmitting and receiving CoordinatedMultipoint (COMP), etc., demands for larger capacity of a controlchannel are increasing.

Accordingly, there is a need for a new control channel design in orderto meet the demands for larger capacity of the control channel.

Technical Problem

An example embodiment of the present invention provides a method oftransmitting downlink control information, capable of satisfying demandsfor a larger capacity of control information in a mobile communicationsystem.

Another example embodiment of the present invention provides a method ofreceiving downlink control information, capable of satisfying demandsfor a larger capacity of control information in a mobile communicationsystem.

Technical Solution

In an example embodiment, there is provided a method in which a basestation transmits downlink control information to a terminal in a mobilecommunication system where a Physical Downlink Control Channel (PDCCH)area is divided from a Physical Downlink Shared Channel (PDSCH) area,the method including: creating the downlink control information;deciding an enhanced Physical Downlink Control Channel (ePDCCH) resourcefor transmitting the downlink control information through the PDSCHarea; and transmitting the downlink control information to the terminalusing the ePDCCH resource.

The ePDCCH may be transmitted through one or both of first and secondslots of a subframe.

In the deciding of the ePDCCH resource for transmitting the downlinkcontrol information, the ePDCCH resource may be specified using at leastone of information about a group of all Physical Resource Blocks (PRBs)through which the ePDCCH is transmitted in the PDSCH area, informationabout a group of UE-specific PRBs through which the ePDCCH istransmitted, among the group of all PRBs, and information about enhancedControl Channel Elements (eCCEs) belonging to the group of UE-specificPRBs.

In the deciding of the ePDCCH resource for transmitting the downlinkcontrol information, at least one of the group of all PRBs and the groupof UE-specific PRBs may be specified to be a UE-specific ePDCCH searchspace of the terminal.

In the deciding of the ePDCCH resource for transmitting the downlinkcontrol information, at least one of the group of all PRBs, the group ofUE-specific PRBs, and the eCCEs belonging to the group of UE-specificPRBs may be decided using at least one of a unique identifier of theterminal and a number of a slot through which the downlink controlchannel is transmitted.

In the deciding of the ePDCCH resource for transmitting the downlinkcontrol information, at least one of the information about the group ofall PRBs, the information about the group of UE-specific PRBs, and theinformation about the eCCEs belonging to the group of UE-specific PRBsmay be transmitted to the terminal using at least one of SystemInformation (SI) broadcasting, Radio Resource Control (RRC) signaling,and a PDCCH.

When the at least one of the information about the group of all PRBs,the information about the group of UE-specific PRBs, and the informationabout the eCCEs belonging to the group of UE-specific PRBs istransmitted to the terminal using the PDCCH, the PDCCH may betransmitted to a UE-specific PDCCH search space of the terminal.

Uplink control information including ACK/NACK information with respectto a PDSCH scheduled based on the downlink control information andtransmitted may be received using a Physical Uplink Control Channel(PUCCH) resource decided by at least ones of numbers assigned to PRBsthrough which the downlink control information has been transmitted,numbers assigned to eCCEs in the PRBs through which the downlink controlinformation has been transmitted, and numbers of antenna ports that havetransmitted the downlink control information.

The PUSCH resource may be decided using a number of an eCCE having thelowest number among eCCEs through which the downlink control informationhas been transmitted.

In another example embodiment, there is provided a method in which aterminal receives downlink control information from a base station in amobile communication system where a Physical Downlink Control Channel(PDCCH) area is divided from a Physical Downlink Shared Channel (PDSCH)area, the method including: deciding an enhanced Physical DownlinkControl Channel (ePDCCH) resource for receiving the downlink controlinformation through the PDSCH area; and receiving the downlink controlinformation using the ePDCCH resource.

Advantageous Effects

According to the method of transmitting and receiving controlinformation, it is possible to cope with increasing requirements for alarger capacity of control information, thereby improving performance ofa mobile communication system.

Also, it is possible to meet the demands for larger capacity of acontrol channel due to Multi-user Multiple Input Multiple Output(MU-MIMO) technology in a heterogeneous network environment, control ofinterference between heterogeneous networks using Carrier Aggregation,frequent use of Multicast-Broadcast Single Frequency Network (MBSFN)subframes, technology of transmitting and receiving CoordinatedMultipoint (COMP), etc. In addition, adaptive resource assignmentaccording to a required capacity of control information is possible,which leads to efficient use of resources.

DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual view explaining the structure of a subframe inwhich a control channel transmission area is divided from a data channeltransmission area.

FIG. 2 is a conceptual view explaining a configuration of a downlinkcontrol channel, according to an example embodiment of the presentinvention.

FIGS. 3 through 5 are conceptual views explaining methods of mappingdownlink control channel transmission resources in a downlink controlchannel transmission method according to an example embodiment of thepresent invention.

FIG. 6 is a conceptual view explaining a transmission location of a newformat of DCI for designating ePDCCH, and the concept of the ePDCCH,according to an example embodiment of the present invention.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

MODE FOR INVENTION

Example embodiments of the present invention are described below insufficient detail to enable those of ordinary skill in the art to embodyand practice the present invention. It is important to understand thatthe present invention may be embodied in many alternate forms and shouldnot be construed as limited to the example embodiments set forth herein.

Accordingly, while the invention can be modified in various ways andtake on various alternative forms, specific embodiments thereof areshown in the drawings and described in detail below as examples. Thereis no intent to limit the invention to the particular forms disclosed.On the contrary, the invention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theappended claims. Elements of the example embodiments are consistentlydenoted by the same reference numerals throughout the drawings anddetailed.

The terminology used herein to describe embodiments of the invention isnot intended to limit the scope of the invention. The articles “a,”“an,” and “the” are singular in that they have a single referent,however the use of the singular form in the present document should notpreclude the presence of more than one referent. In other words,elements of the invention referred to in the singular may number one ormore, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes,” and/or“including,” when used herein, specify the presence of stated features,items, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features, items,steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein are to be interpreted as is customary in the art towhich this invention belongs. It will be further understood that termsin common usage should also be interpreted as is customary in therelevant art and not in an idealized or overly formal sense unlessexpressly so defined herein.

The term “terminal” used in this specification may be referred to asUser Equipment (UE), a User Terminal (UT), a wireless terminal, anAccess Terminal (AT), a Subscriber Unit (SU), a Subscriber Station (SS),a wireless device, a wireless communication device, a WirelessTransmit/Receive Unit (WTRU), a mobile node, a mobile, or other words.The terminal may be a cellular phone, a smart phone having a wirelesscommunication function, a Personal Digital Assistant (PDA) having awireless communication function, a wireless modem, a portable computerhaving a wireless communication function, a photographing device such asa digital camera having a wireless communication function, a gamingdevice having a wireless communication function, a music storing andplaying appliance having a wireless communication function, an Internethome appliance capable of wireless Internet access and browsing, or alsoa portable unit or terminal having a combination of such functions.However, the terminal is not limited to the above-mentioned units.

Also, the term “base station” used in this specification means a fixedor movable node that generally communicates with terminals, and may bereferred to as another word, such as Node-B, eNode-B, a basetransceiversystem (BTS), an access point, a relay, a femto-cell, etc.

Hereinafter, embodiments of the present invention will be described indetail with reference to the appended drawings. In the followingdescription, for easy understanding, like numbers refer to like elementsthroughout the description of the figures, and the same elements willnot be described further.

The following description will be, for convenience of description, givenusing a 3GPP LTE or 3GPP LTE-Advanced system and terms used in 3GPP LTEor 3GPP LTE-Advanced, however, the present invention is not limited tosuch a 3GPP LTE or 3GPP LTE-Advanced system. That is, the 3GPP LTE or3GPP LTE-Advanced system is an exemplary system to which the presentinvention can be applied. For convenience of description, a downlinkphysical control channel is simply referred to as PDCCH (PhysicalDownlink Control Channel), and a downlink physical data channel issimply referred to as PDSCH (Physical Downlink Shared Channel).

FIG. 1 is a conceptual view explaining the structure of a subframe 100in which a PDCCH transmission area 110 is divided from a PDSCHtransmission area 120.

FIG. 1 shows the PDCCH transmission area 110 through which downlinkcontrol information is transmitted, and the PDSCH transmission area 120through which data about terminals is transmitted, defined in 3GPP LTERelease 8 and Release 9 or 3GPP LTE-Advanced Release 10.

Referring to FIG. 1, in the subframe 100, the PDCCH transmission area110 is temporally divided from the PDSCH transmission area 120, and thePDCCH transmission area 110 may be configured with one, two, or threeOFDM symbol durations located in the beginning portion of the subframe100.

However, due to Multi-user Multiple Input Multiple Output (MU-MIMO)technology in a heterogeneous network environment, control ofinterference between heterogeneous networks using Carrier Aggregation,frequent use of Multicast-Broadcast Single Frequency Network (MBSFN)subframes, technology of transmitting and receiving CoordinatedMultipoint (COMP), etc., demands for larger capacity of a controlchannel are increasing.

Accordingly, instead of the method of transmitting control informationthrough a control channel transmission area that uses one to three OFDMsymbols located in the beginning portion of each subframe, there is aneed for a method of transmitting an additional control channel in orderto transmit a large amount of control information.

Method of Transmitting and Receiving a Downlink Control Channel,According to an Example Embodiment of the Present Invention

According to a method of transmitting a downlink control channel, a basestation creates downlink control information that is to be transmittedto a terminal, decides a control channel resource through which thedownlink control information will be transmitted, and transmits thedownlink control information to the terminal using the control channelresource.

The following description about the method of transmitting the downlinkcontrol information to the terminal will be given in view of a basestation, however, a method of receiving downlink control informationwill also be able to be easily understood in view of the terminal basedon the following description.

First, a base station creates downlink control information that is to betransmitted to a terminal, wherein the downlink control informationincludes uplink grant information, uplink scheduling information,downlink resource assignment information, and scheduling information.

Hereinafter, processes of deciding a control channel resource fortransmitting the downlink control information and of transmitting thedownlink control information to the terminal using the control channelresource will be described.

In order to increase the number of physical channels for transmittingdownlink control information or improve performance, the presentinvention is characterized in transmitting an additional control channelthrough the PDSCH transmission area 120 which is a data channeltransmission area for transmission of PDSCH, defined in 3GPP LTE Release8 and Release 9 or 3GPP LTE-Advanced Release 10.

FIG. 2 is a conceptual view explaining a configuration of a downlinkcontrol channel, according to an example embodiment of the presentinvention.

Referring to FIG. 2, in order to distinguish the downlink controlchannel according to the example embodiment from the conventionalphysical downlink control channel (PDCCH) 110, the downlink controlchannel according to the example embodiment will be referred to asePDCCH (enhanced PDCCH) 130.

If a demodulation reference signal (DM-RS) is included in a physicalresource block (PRB) that is transmitted through the ePDCCH 130, a basestation may be configured to apply the same precoding as that applied tothe DM-RS to the ePDCCH 130. The conventional ePDCCH has been designedto be decoded using a Cell-specific RS (CRS), whereas ePDCCH can bedesigned to be decoded using a DM-RS included in a PRB.

Downlink control information (DCI) that is transmitted through theePDCCH 130 may be configured using the same format as DCI defined in3GPP LTE Release 8 and Release 9 or 3GPP LTE-Advanced Release 10. Also,a format for DCI that is transmitted through the ePDCCH 130 may be newlydefined, and the DCI may be transmitted using the newly defined format.

Meanwhile, the ePDCCH 130 may be designed to be transmitted through asingle transmission antenna port or a plurality of transmission antennaports. The numbers of one or more transmission antenna ports throughwhich the ePDCCH 130 is transmitted may be fixed or selected from amongthe numbers of a plurality of possible transmission antenna ports. Atthis time, the transmission antenna port numbers may be decided inconsideration of information about the locations of time and frequencyresources for transmitting the ePDCCH 130, and additional information(terminal identifier such as a Cell Radio Network Temporary Identifier(C-RNTI) or Remote Procedure Call (RPC) signaling information).

If the ePDCCH 130 includes downlink assignment information (for example,scheduling information for PDSCH), the ePDCCH 130 may be mapped tofrequency-time resource elements (REs) using first, second, and thirdmethods as follows.

FIGS. 3 through 5 are conceptual views explaining methods of mappingdownlink control channel transmission resources in a downlink controlchannel transmission method according to an example embodiment of thepresent invention.

In detail, FIG. 3 corresponds to a first method of mapping ePDCCH 131only to a first slot 101 of each subframe, FIG. 4 corresponds to asecond method of mapping ePDCCH 132 to first and second slots 101 and102 of each subframe, and FIG. 5 corresponds to a third method ofmapping ePDCCH 133 only to a second slot 102 of each subframe.

According to the first method, if the ePDCCH 131 is mapped only to thefirst slot of each subframe, PDSCH may be mapped to the second slot at afrequency to which the ePDCCH 131 is mapped. Meanwhile, according to thethird method, if the ePDCCH 133 is mapped to the second slot of eachsubframe, PDSCH may be mapped to the first slot at a frequency to whichthe ePDCCH 133 is mapped.

If ePDCCH includes uplink grant or uplink assignment information (forexample, scheduling information for PUSCH), the ePDCCH may be mapped tofrequency-time REs using one of the first through third methodsdescribed above.

Meanwhile, the first method may be adopted when ePDCCH includes downlinkassignment information or PDSCH scheduling information, and the thirdmethod may be adopted when ePDCCH includes uplink grant or uplinkassignment information. On the contrary, the third method may be adoptedwhen ePDCCH includes downlink assignment information or PDSCH schedulinginformation, and the first method may be adopted when ePDCCH includesuplink grant or uplink assignment information.

Also, ePDCCH may be designed such that each PRB transmits a part or allof ePDCCH for a terminal, or such that each PRB transmits a part or allof ePDCCH for a plurality of terminals.

A method of designing ePDCCH such that each PRB transmits a part or allof ePDCCH for a terminal will be referred to as a “method oftransmitting ePDCCH for a terminal through a PRB”, and a method ofdesigning ePDCCH such that each PRB transmits a part or all of ePDCCHfor a plurality of terminals will be referred to as a “method oftransmitting ePDCCH for two or more terminals through a PRB”.

In both the “method of transmitting ePDCCH for a terminal through a PRB”and the “method of transmitting ePDCCH for two or more terminals througha PRB”, information about a group of PRBs (hereinafter, each referred toas “ePRB (enhanced Physical Resource Block)”) that can be used totransmit ePDCCH may be included in a rule defined in advance between abase station and terminals. Or, the information about the group of ePRBsneeds to be shared between the base station and the terminals by amethod (that is, signaling) in which the base station informs theterminals of the information.

Referring again to FIGS. 3, 4, and 5, a group of all PRBs that a basestation can use to transmit ePDCCH to all terminals belonging to a cellwill be referred to as a “group of all ePDCCH transmittable ePRBs”.Also, an arbitrary PRB belonging to the “group of all ePDCCHtransmittable ePRBs” will be referred to as an ePRB.

Information about such a “group of all ePDCCH transmittable ePRBs” maybe informed to the terminals by the base station through upper layersignaling. The upper layer signaling may be Radio Resource Control (RRC)signaling. Or, information about the “group of all ePDCCH transmittableePRBs” may be transmitted as System Information (SI) to the terminals bythe base station through broadcasting. Or, a new DCI format is designed,information about the “group of all ePDCCH transmittable ePRBs” isincluded in the DCI format, and then, the resultant DCI format istransmitted through PDCCH. This signaling method will be describedlater.

1) Method of Transmitting ePDCCH for Two or More Terminals Through a PRB

In this case, ePDCCH for each terminal may be mapped to REs in unit ofan enhanced Control Channel Element (eCCE). Each eCCE corresponds to Ltime-frequency REs, and the L time-frequency REs belong to a “group ofall ePDCCH transmittable ePRBs”

The L value may be a value near 36. eCCE is different from CCE in thatCCE consists of resource elements existing in an area capable oftransmitting PDCCH in an existing system, and eCCE consists of resourceelements existing in an area capable of transmitting ePDCCH. In the casewhere ePDCCH for an arbitrary terminal is actually transmitted, controlinformation about the terminal may be mapped to one, two, four, or eighteCCEs.

If the number of all eCCEs existing in resource areas (that is, resourceareas in PRBs that can be used to transmit ePDCCH) capable oftransmitting ePDCCH in a k-th subframe is N_(eccE,K), the eCCEs may beassigned from a number 0 to a number N_(eCCE,K)−1.

In this case, the locations of eCCEs to which ePDCCH for each terminalcan be mapped, among all the eCCEs existing in the resource areascapable of transmitting ePDCCH, may be decided by implicit methods orexplicit methods.

According to an example of the implicit methods, the locations of eCCEsto which ePDCCH for each terminal can be mapped may be decided accordingto the RNTI value of the terminal or according to the RNTI value of theterminal and a slot number. Here, RNTI may be C-RNTI, Semi-PersistentScheduling C-RNTI (SPS C-RNTI), System Information-RNTI (SI-RNTI),Paging-RNTI (P-RNTI), or Random Access-RNTI (RA-RNTI).

Also, according to an example of the explicit methods, the locations ofeCCEs to which ePDCCH for each terminal may be designated by RPCsignaling or a newly defined DCI which will be described later.According to another example of the explicit methods, a rule capable ofdeciding eCCE locations is selected by RPC signaling or a newly definedDCI so as to enable each terminal to decide eCCE locations according tothe selected rule.

The locations of eCCEs to which ePDCCH for each terminal can be mappedmay vary depending on a slot number. For example, ePDCCH for anarbitrary terminal may be mapped to eCCEs starting from a third eCCE ata slot number 1, and at a slot number 2, the ePDCCH for the terminal maybe mapped to eCCEs starting from an eighth eCCE.

Accordingly, in the method of transmitting ePDCCH for two or moreterminals through a PRB, information about REs through which ePDCCH istransmitted can be recognized based on information about the “group ofall ePDCCH transmittable ePRBs” and information about eCCEs.

If the “group of all ePDCCH transmittable ePRBs” dynamically changes,information about a “group of all ePDCCH transmittable ePRBs” implicitlyor explicitly signaled and information about eCCEs may be used torecognize information about REs through which ePDCCH is transmitted. Ifthe “group of all ePDCCH transmittable ePRBs” is decided according to arule set in advance between a base station and terminals, onlyinformation about eCCEs may be used to recognize information about REsthrough which ePDCCH is transmitted.

2) Method of Transmitting ePDCCH for a Terminal Through a PRB

First, if ePDCCH includes downlink assignment information or schedulinginformation for PDSCH, the ePDCCH may be transmitted using such resourcemapping methods as the first, second, and third methods described above.

Likewise, if ePDCCH includes uplink grant information or uplinkscheduling information, the ePDCCH may be transmitted using suchresource mapping methods as the first, second and third methodsdescribed above.

As described above, the first method may be adopted when ePDCCH includesdownlink assignment information or scheduling information for PDSCH, andthe third method may be adopted when ePDCCH includes uplink grant oruplink assignment information. On the contrary, the third method may beadopted when ePDCCH includes downlink assignment information, and thefirst method may be adopted when ePDCCH includes uplink grant ordownlink assignment information.

Meanwhile, unlike the method of transmitting ePDCCH for two or moreterminals through a PRB, in the method of transmitting ePDCCH for aterminal through a PRB, instead of designating a location at whichePDCCH will be transmitted in units of eCCE, a location at which ePDCCHwill be transmitted has to be designated in unit of PRB for eachterminal.

Accordingly, in addition to the “group of all ePDCCH transmittableePRBs”, that is, information about all PRBs that a base station can useto transmit ePDCCH to all terminals belonging to a cell, it is necessaryto define ePRB resources to which ePDCCH for an arbitrary user can bemapped, among the “group of all ePDCCH transmittable ePRBs”, as a “groupof UE-specific ePDCCH transmittable ePRBs”.

That is, a base station may transmit ePDCCH for an arbitrary terminalusing some ePRBs of a “group of UE-specific ePDCCH transmittable ePRBs”of the terminal or using all PRBs configuring the “group of UE-specificePDCCH transmittable ePRBs” of the terminal.

Information about the “group of all ePDCCH transmittable ePRBs” or the“group of UE-specific ePDCCH transmittable ePRBs” may be informed to theterminals by the base station through upper layer signaling.

Here, the upper layer signaling may be RRC signaling which will bedescribed later.

Or, by designing a DCI format and including information about the “groupof all ePDCCH transmittable ePRBs” or the “group of UE-specific ePDCCHtransmittable ePRBs” in the DCI format, the information about the “groupof all ePDCCH transmittable ePRBs” or the “group of UE-specific ePDCCHtransmittable ePRBs” may be informed to the terminals, which will bedescribed later.

In order for a terminal to determine whether its own ePDCCH exists ineach subframe, the terminal searches for its own ePDCCH only in the“group of UE-specific ePDCCH transmittable ePRBs” for itself.Accordingly, the “group of UE-specific ePDCCH transmittable ePRBs” is,in view of a terminal, a search space in which the terminal has tosearch to find its own ePDCCH. This process will be described later in aPDCCH and ePDCCH search method of a terminal.

Meanwhile, ePRBs configuring the “group of all ePDCCH transmittableePRBs” or the “group of UE-specific ePDCCH transmittable ePRBs” may becontinuous or discontinuous PRBs on frequency axis.

Also, like the second method of transmitting ePDCCH for a terminalthrough an ePRB, if both the first and second slots of each subframe cantransmit ePDCCH, there are various methods of assigning numbers toePRBs.

One of methods of assigning numbers to ePRBs will be described withreference to FIG. 4. Referring to FIG. 4, ePRBs having lower frequenciesare first assigned ePRB numbers, and at the same frequency, an ePRBcorresponding to a smaller slot number is first assigned an ePRB number.

ePDCCH for a terminal to which the ePDCCH is actually transmitted may besequentially mapped to ePRBs. For example, as illustrated in FIG. 3, ifa base station actually transmits ePDCCH to an arbitrary terminal, thestart location of a resource to which the ePDCCH is mapped is ePRB #1,and the ePDCCH mapped to three ePRBs, ePDCCH for the terminal issequentially mapped to ePRBs #1, #2, and #3.

Method of a Base Station Signaling Transmission Information of ePDCCHfor a Terminal

As described above, in order for a terminal to receive downlink controlinformation, etc. through ePDCCH, a base station has to inform theterminal of information about ePDCCH in advance. The base station mayinform the terminal of information about ePDCCH using one of the methodsas follows:

(Method A) Method of Informing Scheduling Information of ePDCCH ThroughRRC Signaling.

A base station may be configured to inform a terminal of schedulinginformation of ePDCCH through RRC signaling. Here, the schedulinginformation of ePDCCH may include information about time and/orfrequency resources through which ePDCCH (that is, eCCE resources towhich control information is mapped) is transmitted. In this case, sincethe base station uses RRC signaling to directly inform the terminal oflocations of resources through which ePDCCH is transmitted, the terminalcan acquire downlink control information from resources at locationsindicated by RRC signaling, without having to search for ePDCCH areas.

As a method of modulating control information that is transmittedthrough ePDCCH, a BPSK or QPSK method may be used for robusttransmission, or through RRC signaling, modulation and coding scheme(MCS) information may be informed. In addition, scheduling informationmay include rank information for the ePDCCH. Also, schedulinginformation may include information about a transmission antenna portfor the ePDCCH.

If PDSCH and ePDCCH are simultaneously transmitted using the sametime-frequency resources through different antenna ports (that is,different antenna layers), RRC signaling may be used to inform theterminal of the simultaneous transmission of the PDSCH, or of rankinformation for the PDSCH or information about the transmission antennaports.

(Method B) Method of Informing Scheduling Information of ePDCCH ThroughNew Downlink Control Information

Another method in which a base station informs a terminal of schedulinginformation of ePDCCH is to use downlink control information having anew format (that is, a new DCI format for representing schedulinginformation of ePDCCH, which is different from existing DCI formats, isdefined). A control channel for transmitting the new DCI format mayexist in a PDCCH transmission area defined in 3GPP LTE Release 8 andRelease 9 or LTE-Advanced Release 10.

FIG. 6 is a conceptual view explaining ePDCCH 130 and a new format ofDCI 111 for designating the ePDCCH 130, according to an exampleembodiment of the present invention.

Referring to FIG. 6, a control channel for transmitting the new formatof DCI 111 may exist in one, two or three OFDM symbol areas, startingfrom the beginning portion of each subframe.

The new format of DCI 111 includes scheduling information of the ePDCCH130. The scheduling information of the ePDCCH 130 includes informationabout time and/or frequency resources through which the ePDCCH 130 istransmitted. Also, the scheduling information may include MCSinformation for the ePDCCH 130.

Also, scheduling information may include rank information for the ePDCCH130 or information about transmission antenna ports transmitting theePDCCH 130. If PDSCH and the ePDCCH 130 are simultaneously transmittedusing the same time and frequency resources, the scheduling informationmay include information indicating that PDSCH is transmitted togetherwith the ePDCCH 130, or the scheduling information may inform of rankinformation for the PDSCH or information about transmission antennaports transmitting the PDSCH.

At this time, the control channel (PDSCCH) for transmitting the newformat of DCI 111 may exist in a UE-specific search space among areas inwhich a terminal has to search to find PDCCH transmitted to itself.

(Method C) Method of Informing Information about ePDCCH TransmittableAreas Through RRC Signaling.

According to method C, a base station directly informs a terminal ofinformation about both a “group of all ePDCCH transmittable ePRBs” and a“group of UE-specific ePDCCH transmittable ePRBs” through RRC signaling,or explicitly informs the terminal of information about one of the“group of all ePDCCH transmittable ePRBs” and the “group of UE-specificePDCCH transmittable ePRBs” through RRC signaling.

Method C performs signaling using one of the methods as follows:

According to one of the methods, a base station informs each terminal ofinformation about a “group of all ePDCCH transmittable ePRBs”, and theterminal searches for a “group of UE-specific ePDCCH transmittableePRBs” for itself in the “group of all ePDCCH transmittable ePRBs” usingits own RNTI value or using its own RNTI value and a slot number.

Also, the frequencies of the ePRBs configuring the “group of all ePDCCHtransmittable ePRBs” may not change with respect to each subframe untila new signal is received. In other words, the “group of all ePDCCHtransmittable ePRBs” is maintained as the most recently receivedinformation until a new signal is received.

In order for the terminal to determine whether ePDCCH for itself existsin each subframe, the terminal searches for the ePDCCH only in the“group of UE-specific ePDCCH transmittable ePRBs”. Accordingly, in viewof the terminal, the “group of ePDCCH transmittable ePRBs” becomes anePDCCH search space for the terminal.

According to another one of the methods, a base station directly informseach terminal of a “group of UE-specific ePDCCH transmittable ePRBs”using UE-specific parameters. In this case, the terminal can acquire the“group of UE-specific ePDCCH transmittable ePRBs” for itself throughsignaling received from the base station, and determines whether ePDCCHfor itself has been actually transmitted in the “group of UE-specificePDCCH transmittable ePRBs”.

The base station may inform a plurality of terminals of different“groups of UE-specific ePDCCH transmittable ePRBs”, respectively, or maygroup a plurality of terminals into several groups and inform each groupof the same “group of UE-specific ePDCCH transmittable ePRBs”. Also, thefrequencies of the ePRBs configuring the “group of UE-specific ePDCCHtransmittable ePRBs” may not change with respect to each subframe untila new signal is received. In other words, the “group of UE-specificePDCCH transmittable ePRBs” for the corresponding terminal is maintainedas the most recently received information until a new signal isreceived.

Also, signaling information may include MCS information about controlinformation that is transmitted through the ePDCCH. The signalinginformation may include rank information for the ePDCCH or informationabout transmission antenna ports.

PDCCH and ePDCCH Search Method of a Terminal

According to 3GPP LTE Release 8 and Release 9 or LTE-Advanced Release10, each terminal searches for a “common search space” and a“UE-specific search space” in order to find PDCCH transmitted to itself,wherein the “common search space” is a space which all terminals searchin common, and the “UE-specific search space” is a space which only thespecific terminal can search. According to the method of transmittingand receiving DCI, as described above, ePDCCH transmission areas decidedby signaling of a base station or by an implicit method can beunderstood to be included in the “UE-specific search space”.

Also, as described above, DCI that is transmitted through ePDCCH may beconfigured using the same format as DCI defined in 3GPP LTE Release 8and Release 9 or LTE-Advanced Release 10. Alternatively, it is alsopossible to define a new format for DCI that is transmitted throughePDCCH, and transmit the DCI using the newly defined format, wherein thenewly defined DCI format is distinguished from the newly defined DCIformat for signaling ePDCCH areas as described above with reference toFIG. 6.

Hereinafter, a method in which a terminal searches for a newly definedformat of DCI for indicating an ePDCCH transmission area, and a methodin which the terminal searches for DCI transmitted through an ePDCCHtransmission area in the ePDCCH transmission area will be described.

First, the method in which the terminal searches for the newly definedformat of DCI will be described below.

The method in which the terminal searches for the newly defined formatof DCI (that is, DCI for indicating an ePDCCH transmission area), asillustrated in FIG. 6, may be one of the methods as follows:

(Method A) Method of enabling a terminal to search for an existing DCIformat in a UE-specific search space. That is, method A prevents a newformat of DCI from being transmitted through an existing PDCCH area.Accordingly, method A is used in the case of using no ePDCCH or in thecase of signaling existence of ePDCCH using a different method (forexample, RRC signaling) from the method of using a new format of DCI.

(Method B) Method of enabling a terminal to search for a new format ofDCI in a UE-specific search space. That is, method B is to transmit anew format of DCI through a UE-specific search space of an existingPDCCH area, while transmitting no new format of DCI through a commonsearch space.

(Method C) Method of enabling a terminal to search for both an existingformat of DCI and a new format of DCI in a UE-specific search space.That is, method C is configured to transmit all the existing format ofDCI and the new format of DCI through a UE-specific search space.

In methods A, B, and C, a base station may inform the terminal that theterminal has to search for an existing format of DCI in the UE-specificsearch space, or that the terminal has to search for a new format of DCIin the UE-specific search space, through signaling. The signaling may beRRC signaling.

Then, a method in which a terminal searches for an ePDCCH area will bedescribed below.

The terminal searches for a common search space in an existing PDCCHarea in order to check whether there is a control channel transmitted toitself, and also, the terminal searches for an ePDCCH search space arearecognized through RRC signaling. That is, an ePDCCE transmission areadecided by signaling of a base station or by an implicit method can beunderstood to be included in a “UE-specific search space”.

As described above, a method in which the base station informs theterminal of the ePDCCH search space may be signaled using one of themethods as follows.

According to one of the methods, a base station informs each terminal ofa “group of all ePDCCH transmittable ePRBs”, and the terminal searchesfor a “group of UE-specific ePDCCH transmittable ePRBs” for itself inthe “group of all ePDCCH transmittable ePRBs”, using its own RNTI valueor using its own RNTI value and a slot number. The terminal searches forePDCCH only in the “group of UE-specific PDCCH transmittable ePRBs” inorder to check whether ePDCCH for itself exists in each subframe.Accordingly, in view of the terminal, the “group of UE-specific ePDCCHtransmittable ePRBs” becomes an ePDCCH search space for the terminal.

According to another one of the methods, a base station informs eachterminal of a “group of UE-specific ePDCCH transmittable ePRBs” using aUE-specific parameter. The terminal searches for ePDCCH in the “group ofUE-specific ePDCCH transmittable ePRBs” for itself.

Method of Designing ePDCCH when there are a Plurality of Transmissionand Reception Points

An environment where a plurality of transmission/reception points aregeographically distant from each other in the same cell and eachtransmission/reception point has one or more transmission/receptionantennas is considered. Specifically, an environment which a pluralityof transmission points belongs to the same cell and have the same cellID is considered. The transmission/reception points may be referred toas Remote Radio Heads (RRHs) or Remote Radio Units (RRUs). The RRHs areconnected to a base station through optical fiber or microwave, etc. soas to receive/transmit information from/to the base station.

In the environment, a method of creating ePDCCH will be described below.

Bit-level scrambling may be used to create ePDCCH. At this time, inorder to reuse ePDCCH resources between transmission points, virtualcell IDs may be used. That is, transmission points belonging to the samecell and having the same cell ID may be assigned different virtual cellIDs. Accordingly, a method of creating a scrambling sequence forbit-level scrambling on ePDCCH is to create a scrambling sequence usingthe virtual cell IDs of transmission points of transmitting ePDCCH,instead of using a cell ID. Another method of creating a scramblingsequence for bit-level scrambling on ePDCCH is to create a scramblingsequence using a cell ID.

In order to create PDCCH for transmitting a new format of DCI, bit-levelscrambling may also be used. At this time, one method of creating ascrambling sequence for bit-level scrambling on the PDCCH is to createthe scrambling sequence using a cell ID. Another method of creating ascrambling sequence for bit-level scrambling on the PDCCH is to create ascrambling sequence using the virtual cell ID of a transmission point oftransmitting PDCCH, instead of using the cell ID.

Method of Designing a Physical Uplink Control Channel (PUCCH)

In order to transmit ACK/NACK information with respect to PDSCHscheduled by ePDCCH described above to PUCCH, it is necessary to set arelationship between the PDSCH scheduled by the ePDCCH and the PUCCH towhich the ACK/NACK information with respect to the PDSCH is transmitted.

Hereinafter, a method of transmitting ACK/NACK (or, ACK/NAK) informationwith respect to PDSCH scheduled by ePDCCH to PUCCH will be described.

Specifically, a PUCCH transmission method when ePDCCH is transmittedthrough one antenna port and thus PDSCH scheduled by the ePDCCH is alsotransmitted through one antenna port will be first described, below.

1) Method of Transmitting ACK/NACK Information with Respect to PDSCHScheduled by ePDCCH that is Transmitted by the Method of TransmittingePDCCH for Two or More Terminals Through a PRB.

As described above, in the method of transmitting ePDCCH for two or moreterminals through a PRB, a part or all of ePDCCH for a plurality ofterminals may be interleaved in each ePRB and transmitted. At this time,control information of each terminal, which is transmitted to ePDCCH, ismapped to time-frequency resources in units of eCCE.

First, in order to transmit ACK/NACK information with respect to PDSCHscheduled by ePDCCH, a case of transmitting PUCCH using a transmissionantenna port will be described.

If a transmission antenna port that is used for transmitting PUCCH isp₀, a PUCCH resource n_(PUCCH) ^((1,p=p) ⁰ ⁾ for the transmissionantenna port p₀ may be configured according to Equation 1, below:n _(PUCCH) ^((1,p=p) ⁰ ⁾ =n _(eCCE) ^((ePDCCH)) +N _(PUCCH)^((e,1)),  (1)where n_(eCCE) ^((ePDCCH)) represents the lowest eCCE index among eCCEsconfiguring ePDCCH including scheduling information of the PDSCH, andN_(PUCCH) ^((e,1)) represents a parameter configured by the upper layerand may be provided by RRC.

That is, Equation 1 means that ACK/NACK information with respect toPDSCH scheduled by ePDCCH transmitted using eCCEs starting from n_(eCCE)^((ePDCCH)) is transmitted using a PUCCH resource n_(PUCCH) ^((1,p=p) ⁰⁾.

Next, a case of using two transmission antenna ports in order totransmit ACK/NACK information with respect to PDSCH scheduled by ePDCCHwill be described. That is, the case may correspond to the case oftransmitting the same ACK/NACK information using two transmissionantenna ports.

In this case, PUCCH resources n_(PUCCH) ^((1,p=p) ⁰ ⁾ and n_(PUCCH)^((1,p=p) ¹ ⁾ for two transmission antenna ports p₀ and p₁ may beconfigured as follows. In regard of the transmission antenna port p₀,the same method used in the case where a transmission antenna port isused, as described above, may be used. That is, the PUCCH resourcen_(PUCCH) ^((1,p=p) ⁰ ⁾ can be configured according to Equation 2,below:n _(PUCCH) ^((1,p=) ⁰ ⁾ =n _(eCCE) ^((ePDCCH)) +N _(PUCCH) ^((e,1))  (2)

In regard of the other transmission antenna port p₁, the PUCCH resourcen_(PUCCH) ^((1,p=p) ¹ ⁾ can be configured according to Equation 3,below:n _(PUCCH) ^((1,p=p) ¹ ⁾ =n _(eCCE) ^((ePDCCH)) +M ₁ +N _(PUCCH)^((e,1))  (3)where M₁ is a constant, and for example, M₁=1.

Now, a method of setting N_(PUCCH) ^((e,1)) will be described. TheN_(PUCCH) ^((e,1)) may be set by the upper layer, according to one ofmethods as follows:

(Method A) Method of Setting the Same N_(PUCCH) ^((e,1)) for allTerminals

Method A is to set the same N_(PUCCH) ^((e,1)) for all terminals. Thatis method A is to configure the N_(PUCCH) ^((e,1)) using a cell-specificparameter for all terminals. For this, a cell-specific parameter that isapplied in common to all terminals, among RRC parameters, may be used toinform the terminals. Another method of configuring the same N_(PUCCH)^((e,1)) for all terminals is to set UE-specific parameters for allterminals to the same value.

(Method B) Method of Configuring the N_(PUCCH) ^((e,1)) UsingUE-Specific Parameters.

Method B is to inform terminals of the N_(PUCCH) ^((e,1)) usingUE-specific parameters. That is, the N_(PUCCH) ^((e,1)) is informed toterminals using UE-specific parameters among RRC parameters. Method Bincludes a method of grouping terminals into several groups and settingthe same value for each group.

2) Method of Transmitting ACK/NACK Information with Respect to PDSCHScheduled by ePDCCH Transmitted by the Method of Transmitting ePDCCH fora Terminal Through a PRB.

As described above, in the method of transmitting ePDCCH for a terminalthrough a PRB, a part or all of ePDCCH for a terminal can be transmittedthrough each ePRB. At this time, control information of each terminal,which is transmitted to the ePDCCH, is mapped to time-frequencyresources in units of ePRB. That is, ePDCCH for each terminal may beconfigured in units of ePRB.

A case of using a transmission antenna port in order to transmitACK/NACK information with respect to PDSCH scheduled by ePDCCH to PUCCHwill be first described below. The transmission antenna port is given asp0.

A PUCCH resource n_(PUCCH) ^((1,p=p) ⁰ ⁾ for the transmission antennaport p₀ can be configured according to Equation 4, below:n _(PUCCH) ^((1,p=p) ⁰ ⁾ =n _(ePRB) ^((ePDCCH)) +N _(PUCCH)^((e,2))  (4)where n_(eCCE) ^((ePDCCH)) represents the lowest eCCE index among eCCEsconfiguring ePDCCH of the corresponding terminal. For example, if ePDCCHis mapped to ePRBs #2, #3, and #4 in the method illustrated in FIG. 3,4, or 5, n_(eCCCE) ^((ePDCCH)) is 2.

A case of using two transmission antenna ports p0 and p1 in order totransmit ACK/NACK information with respect to ePDSCH scheduled by thePDCCH to PUCCH will be described below.

A PUCCH resource n_(PUCCH) ^((1,p=p) ⁰ ⁾ for the transmission antennaport p₀ may be configured in the same method as used in the case where atransmission antenna port is used. That is, the PUCCH resource n_(PUCCH)^((1,p=p) ⁰ ⁾ can be configured according to Equation 5, below:n _(PUCCH) ^((1,p=p) ⁰ ⁾ =n _(ePRB) ^((ePDCCH)) +N _(PUCCH)^((e,2))  (5)

A PUCCH resource n_(PUCCH) ^((1,p=p) ¹ ⁾ for the other transmissionantenna port p1 can be configured according to Equation 6, below:n _(PUCCH) ^((1,p=p) ¹ ⁾ =n _(ePRB) ^((ePDCCH)) +N _(PUCCH)^((e,2)).  (6)where M₂ is a constant, and for example, M₂=1.

N_(PUCCH) ^((e,2)) represents a parameter configured by the upper layerand may be provided by RRC. The N_(PUCCH) ^((e,2)) may be configuredusing one of the methods as follows:

(Method A) Method of Configuring the Same N_(PUCCH) ^((e,2)) for allTerminals

Method A is to configure the same N_(PUCCH) ^((e,2)) for all terminals.For this, a cell-specific parameter that is applied in common to allterminals, among RRC parameters, may be used to inform the terminals.Another method of configuring the same N_(PUCCH) ^((e,1)) for allterminals is to set UE-specific parameters for all terminals to the samevalue.

(Method B) Method of Configuring N_(PUCCH) ^((e,2)) Using UE-SpecificParameters

Method B is to inform terminals of N_(PUCCH) ^((e,2)) using UE-specificparameters. That is, the is informed to terminals using UE-specificparameters among RRC parameters. Method B includes a method of groupingterminals into several groups and setting the same value for allterminals belonging to each group.

Next, a case where one or more PDCCHs are transmitted through the sametime-frequency resources using several transmission antenna ports orusing a part of several possible transmission antenna ports, will bedescribed.

In this case, a plurality of ePDCCHs may include control information ofa terminal or control information of a plurality of terminals. A casewhere the plurality of ePDCCHs are transmitted through the sametime-frequency resources using different transmission antenna ports willbe first described, below.

It is assumed that ePDCCH including scheduling information for arbitraryPDSCH has been transmitted through a Q_(ePDCCH)-th transmission antennaport of a base station.

First, a case of using a transmission antenna port in order to transmitACK/NACK information with respect to PDSCH scheduled by ePDCCH to PUCCHis described.

In this case, if the transmission antenna port used to transmit PUCCH isp₀, a PUCCH resource n_(PUCCH) ^((1,p=p) ⁰ ⁾ for the transmissionantenna port p₀ can be configured according to Equation 7, below:n _(PUCCH) ^((1,p=p) ⁰ ⁾ =n _(ePRB) ^((ePDCCH)) +N _(PUCCH) ^((e,2)) +N_(ePDCCH) ·A _(PORT)  (7)

Meanwhile, Equation 7 corresponds to the method of transmitting ePDCCHfor a terminal through a PRB, and if Equation 7 is rewritten byreplacing n_(ePRB) ^((ePDCCH)) with n_(eCCE) ^((ePDCCH)), Equation 7corresponds to the method of transmitting ePDCCH for two or moreterminals through a PRB.

In Equation 7, A_(PORT) is information about a transmission antenna portq for the corresponding ePDCCH. A method of setting A_(PORT) is asfollows. For example, if a Q_(ePDCCH)-th transmission antenna port amongall transmission antenna ports that can be used to transmit ePDCCH hasbeen used, A_(PORT)=(Q_(ePDCCH)−1). That is, if the first transmissionantenna port has been used, A_(PORT)=0.

Also, a method of setting N_(ePDCCH) is to set N_(ePDCCH) to 1. Anothermethod of setting N_(ePDCCH) is for a base station to inform terminalsof N_(ePDCCH) through upper layer signaling. At this time, the upperlayer signaling may be RRC signaling. When the base station informsterminals of N_(ePDCCH), the base station may inform all the terminalsof a common value using a cell-specific parameter, or may inform therespective terminals of UE-specific values using UE-specific parameters.

Now, a case of using two transmission antenna ports p₀ and p₁ in orderto transmit ACK/NACK information with respect to PDSCH scheduled byePDCCH to PUCCH is described.

In regard of a PUCCH resource n_(PUCCH) ^((1,p=p) ⁰ ⁾ for thetransmission antenna port p₀, the same method used in the case where atransmission antenna port is used, as described above, may be used. Thatis, the PUCCH resource n_(PUCCH) ^((1,p=p) ⁰ ⁾ can be configuredaccording to Equation 8, below:n _(PUCCH) ^((1,p=p) ⁰ ⁾ =n _(ePRB) ^((ePDCCH)) +N _(PUCCH) ^((e,2)) +N_(ePDDCH) ·A _(PORT)  (8)

Equation 8 corresponds, like Equation 7, to the method of transmittingePDCCH for a terminal through a PRB, and if Equation 8 is rewritten byreplacing n_(ePRB) ^((ePDCCH)) with n_(eCCE) ^((ePDCCH)), Equation 8corresponds to the method of transmitting ePDCCH for two or moreterminals through a PRB.

A PUCCH resource n_(PUCCH) ^((1,p=p) ¹ ⁾ for the other transmissionantenna port p₁ can be configured according to Equation 9, below:n _(PUCCH) ^((1,p=p) ¹ ⁾ =n _(ePRB) ^((ePDCCH)) +M ₂ +N _(PUCH) ^((e,2))+N _(ePDCCH) ·A _(PORT)  (9)

In Equation 9, M₃ is a constant, and for example, M₃=1.

A number of examples have been described above. Nevertheless, it will beunderstood that various modifications may be made. For example, suitableresults may be achieved if the described techniques are performed in adifferent order and/or if components in a described system,architecture, device, or circuit are combined in a different mannerand/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

The invention claimed is:
 1. A method for transmitting downlink controlinformation to a terminal through a radio frame, the radio framecomprising a plurality of subframes, each subframe comprising at leasttwo slots, each subframe being divided in time domain into a first areaand a second area, wherein a first physical downlink control channel islocated in the first area, a physical downlink shared channel is locatedin the second area and the first physical downlink control channel isnot located in the second area, the method comprising: transmitting, tothe terminal, scheduling information related to a second physicaldownlink control channel; and transmitting the downlink controlinformation to the terminal through the second physical downlink controlchannel, wherein the second physical downlink control channel is locatedin the second area, wherein location of the downlink control informationin the second area is determined at least based on a slot number of oneof the slots within the radio frame, wherein the downlink controlinformation is located in the one of the slots.
 2. The method of claim1, wherein the scheduling information is transmitted through upper layersignaling.
 3. The method of claim 2, wherein the upper layer signalingis Radio Resource Control (RRC) signaling.
 4. The method of claim 1,wherein the location of the downlink control information in the secondarea is determined based also on an identifier of the terminal.
 5. Themethod of claim 4, wherein the identifier of the terminal is a RadioNetwork Temporary Identifier (RNTI) of the terminal.
 6. The method ofclaim 4, wherein the location of the downlink control information in thesecond area corresponds to a terminal-specific search space for theterminal.
 7. The method of claim 1, wherein the second physical downlinkcontrol channel is modulated by Quadrature Phase Shift Keying (QPSK). 8.The method of claim 1, wherein a same precoding as that applied to ademodulation reference signal (DM-RS) is applied to the second physicaldownlink control channel.
 9. A method for receiving downlink controlinformation from a base station through a radio frame, the radio framecomprising a plurality of subframes, each subframe comprising at leasttwo slots, each subframe being divided in time domain into a first areaand a second area, wherein a first physical downlink control channel islocated in the first area, a physical downlink shared channel is locatedin the second area and the first physical downlink control channel isnot located in the second area, the method comprising: receiving, fromthe base station, scheduling information related to a second physicaldownlink control channel; and receiving the downlink control informationfrom the base station through the second physical downlink controlchannel, wherein the second physical downlink control channel is locatedin the second area, wherein location of the downlink control informationin the second area is determined at least based on a slot number of oneof the slots within the radio frame, wherein the downlink controlinformation is located in the one of the slots.
 10. The method of claim9, wherein the first physical downlink control channel corresponds to acommon search space for the terminal.
 11. The method of claim 9, whereinthe scheduling information is received through upper layer signaling.12. The method of claim 11, wherein the upper layer signaling is RadioResource Control (RRC) signaling.
 13. The method of claim 9, wherein thelocation of the downlink control information in the second area isdetermined based also on an identifier of the terminal.
 14. The methodof claim 13, wherein the identifier of the terminal is a Radio NetworkTemporary Identifier (RNTI) of the terminal.
 15. The method of claim 13,wherein the location of the downlink control information in the secondarea corresponds to a terminal-specific search space for the terminal.16. The method of claim 9, wherein the second physical downlink controlchannel is modulated by Quadrature Phase Shift Keying (QPSK).
 17. Themethod of claim 9, wherein a same precoding as that applied to ademodulation reference signal (DM-RS) is applied to the second physicaldownlink control channel.
 18. A method for transmitting downlink controlinformation to a terminal through a radio frame comprising a pluralityof subframes each comprising a first and a second slots, each subframeincluding frequency-time multiplexed resource elements which are dividedin time domain into a first area for a first physical downlink controlchannel and a second area for a first physical downlink shared channel,the method comprising: transmitting, to the terminal, schedulinginformation about a second physical downlink control channel; andtransmitting the downlink control information through the secondphysical downlink control channel to the terminal in accordance with thescheduling information, wherein the scheduling information about thesecond physical downlink control channel includes information about agroup of resource blocks through which the downlink control informationmay be transmitted, each resource block in the group of resource blockscomprising a plurality of resource elements, wherein the first physicaldownlink shared channel and the second physical downlink control channelshares the second area, and wherein location of a resource element inthe group of resource blocks through which the downlink controlinformation for the terminal is transmitted is determined at least basedon a slot number of a slot in the radio frame to which the resourceelement belongs.
 19. The method of claim 18, wherein the location of theresource element in the group of the resource blocks through which thedownlink control information for the terminal is transmitted isdetermined based also on an identifier of the terminal.
 20. The methodof claim 19, wherein the identifier of the terminal is a Radio NetworkTemporary Identifier (RNTI) of the terminal.
 21. The method of claim 18,wherein the resource element in the group of the resource blocks throughwhich the downlink control information for the terminal is transmittedcorresponds to a terminal-specific search space for the terminal. 22.The method of claim 18, wherein the second physical downlink controlchannel is modulated by Quadrature Phase Shift Keying (QPSK).
 23. Amethod for receiving downlink control information from a base stationthrough a radio frame comprising a plurality of subframes eachcomprising a first and a second slots, each subframe includingfrequency-time multiplexed resource elements which are divided in timedomain into a first area for a first physical downlink control channeland a second area for a first physical downlink shared channel, themethod comprising: receiving, from the base station, schedulinginformation about a second physical downlink control channel; andreceiving the downlink control information through the second physicaldownlink control channel from the base station in accordance with thescheduling information, wherein the scheduling information about thesecond physical downlink control channel includes information about agroup of resource blocks through which the downlink control informationmay be transmitted, each resource block in the group of resource blockscomprising a plurality of resource elements, wherein the first physicaldownlink shared channel and the second physical downlink control channelshares the second area, and wherein location of a resource element inthe group of resource blocks through which the downlink controlinformation for the terminal is transmitted is determined at least basedon a slot number of a slot in the radio frame to which the resourceelement belongs.
 24. The method of claim 23, wherein the first physicaldownlink control channel corresponds to a common search space for theterminal.
 25. The method of claim 24, wherein the resource element inthe group of the resource blocks through which the downlink controlinformation for the terminal is transmitted corresponds to aterminal-specific search space for the terminal.
 26. The method of claim23, wherein the location of the resource element in the group of theresource blocks through which the downlink control information for theterminal is received is determined based also on an identifier of theterminal.
 27. The method of claim 26, wherein the identifier of theterminal is a Radio Network Temporary Identifier (RNTI) of the terminal.28. The method of claim 23, wherein the second physical downlink controlchannel is modulated by Quadrature Phase Shift Keying (QPSK).
 29. Aterminal for receiving downlink control information from a base stationthrough a radio frame comprising a plurality of subframes eachcomprising a first and a second slots, each subframe includingfrequency-time multiplexed resource elements which are divided in timedomain into a first area for a first physical downlink control channeland a second area for a first physical downlink shared channel, theterminal being configured to: receive, from the base station, schedulinginformation about a second physical downlink control channel; andreceive the downlink control information through the second physicaldownlink control channel from the base station in accordance with thescheduling information, wherein the scheduling information about thesecond physical downlink control channel includes information about agroup of resource blocks through which the downlink control informationmay be transmitted, each resource block in the group of resource blockscomprising a plurality of resource elements, wherein the first physicaldownlink shared channel and the second physical downlink control channelshares the second area, and wherein location of a resource element inthe group of resource blocks through which the downlink controlinformation for the terminal is transmitted is determined at least basedon a slot number of a slot in the radio frame to which the resourceelement belongs.
 30. The terminal of claim 29, wherein the firstphysical downlink control channel corresponds to a common search spacefor the terminal.
 31. The terminal of claim 30, wherein the resourceelement in the group of the resource blocks through which the downlinkcontrol information for the terminal is transmitted corresponds to aterminal-specific search space for the terminal.
 32. The terminal ofclaim 29, wherein the location of the resource element in the group ofthe resource blocks through which the downlink control information forthe terminal is received is determined based also on an identifier ofthe terminal.
 33. The terminal of claim 32, wherein the identifier ofthe terminal is a Radio Network Temporary Identifier (RNTI) of theterminal.
 34. The terminal of claim 29, wherein the second physicaldownlink control channel is modulated by Quadrature Phase Shift Keying(QPSK).